Re: [Xen-devel] [PATCH v8 for-4.9 1/5] hvm/dmop: Box dmop_args rather than passing multiple parameters around

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jennifer,

I don't see any cover letter for this series, so I will answer here.

Looking at the code, it looks like a new feature rather than a bug fix. 
Am I right?
Could you explain what would be the benefits and risks to get this code 
in the release?
I also like to hear the opinion of the x86 maintainers about getting 
this code in Xen 4.9.
Cheers,

On 21/04/17 15:05, jennifer.herbert@xxxxxxxxxx wrote:
> From: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>
>
> No functional change.
>
> Signed-off-by: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
>
> --
> CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> ---
> No change.
> ---
>  xen/arch/x86/hvm/dm.c | 49 +++++++++++++++++++++++++++++--------------------
>  1 file changed, 29 insertions(+), 20 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
> index d72b7bd..e583e41 100644
> --- a/xen/arch/x86/hvm/dm.c
> +++ b/xen/arch/x86/hvm/dm.c
> @@ -25,6 +25,13 @@
>
>  #include <xsm/xsm.h>
>
> +struct dmop_args {
> +    domid_t domid;
> +    unsigned int nr_bufs;
> +    /* Reserve enough buf elements for all current hypercalls. */
> +    struct xen_dm_op_buf buf[2];
> +};
> +
>  static bool copy_buf_from_guest(const xen_dm_op_buf_t bufs[],
>                                  unsigned int nr_bufs, void *dst,
>                                  unsigned int idx, size_t dst_size)
> @@ -56,7 +63,7 @@ static bool copy_buf_to_guest(const xen_dm_op_buf_t bufs[],
>  }
>
>  static int track_dirty_vram(struct domain *d, xen_pfn_t first_pfn,
> -                            unsigned int nr, struct xen_dm_op_buf *buf)
> +                            unsigned int nr, const struct xen_dm_op_buf *buf)
>  {
>      if ( nr > (GB(1) >> PAGE_SHIFT) )
>          return -EINVAL;
> @@ -287,16 +294,14 @@ static int inject_event(struct domain *d,
>      return 0;
>  }
>
> -static int dm_op(domid_t domid,
> -                 unsigned int nr_bufs,
> -                 xen_dm_op_buf_t bufs[])
> +static int dm_op(const struct dmop_args *op_args)
>  {
>      struct domain *d;
>      struct xen_dm_op op;
>      bool const_op = true;
>      long rc;
>
> -    rc = rcu_lock_remote_domain_by_id(domid, &d);
> +    rc = rcu_lock_remote_domain_by_id(op_args->domid, &d);
>      if ( rc )
>          return rc;
>
> @@ -307,7 +312,7 @@ static int dm_op(domid_t domid,
>      if ( rc )
>          goto out;
>
> -    if ( !copy_buf_from_guest(bufs, nr_bufs, &op, 0, sizeof(op)) )
> +    if ( !copy_buf_from_guest(&op_args->buf[0], op_args->nr_bufs, &op, 0, 
> sizeof(op)) )
>      {
>          rc = -EFAULT;
>          goto out;
> @@ -466,10 +471,10 @@ static int dm_op(domid_t domid,
>          if ( data->pad )
>              break;
>
> -        if ( nr_bufs < 2 )
> +        if ( op_args->nr_bufs < 2 )
>              break;
>
> -        rc = track_dirty_vram(d, data->first_pfn, data->nr, &bufs[1]);
> +        rc = track_dirty_vram(d, data->first_pfn, data->nr, &op_args->buf[1]);
>          break;
>      }
>
> @@ -564,7 +569,7 @@ static int dm_op(domid_t domid,
>
>      if ( (!rc || rc == -ERESTART) &&
>           !const_op &&
> -         !copy_buf_to_guest(bufs, nr_bufs, 0, &op, sizeof(op)) )
> +         !copy_buf_to_guest(&op_args->buf[0], op_args->nr_bufs, 0, &op, 
> sizeof(op)) )
>          rc = -EFAULT;
>
>   out:
> @@ -587,20 +592,21 @@ CHECK_dm_op_set_mem_type;
>  CHECK_dm_op_inject_event;
>  CHECK_dm_op_inject_msi;
>
> -#define MAX_NR_BUFS 2
> -
>  int compat_dm_op(domid_t domid,
>                   unsigned int nr_bufs,
>                   XEN_GUEST_HANDLE_PARAM(void) bufs)
>  {
> -    struct xen_dm_op_buf nat[MAX_NR_BUFS];
> +    struct dmop_args args;
>      unsigned int i;
>      int rc;
>
> -    if ( nr_bufs > MAX_NR_BUFS )
> +    if ( nr_bufs > ARRAY_SIZE(args.buf) )
>          return -E2BIG;
>
> -    for ( i = 0; i < nr_bufs; i++ )
> +    args.domid = domid;
> +    args.nr_bufs = nr_bufs;
> +
> +    for ( i = 0; i < args.nr_bufs; i++ )
>      {
>          struct compat_dm_op_buf cmp;
>
> @@ -610,12 +616,12 @@ int compat_dm_op(domid_t domid,
>  #define XLAT_dm_op_buf_HNDL_h(_d_, _s_) \
>          guest_from_compat_handle((_d_)->h, (_s_)->h)
>
> -        XLAT_dm_op_buf(&nat[i], &cmp);
> +        XLAT_dm_op_buf(&args.buf[i], &cmp);
>
>  #undef XLAT_dm_op_buf_HNDL_h
>      }
>
> -    rc = dm_op(domid, nr_bufs, nat);
> +    rc = dm_op(&args);
>
>      if ( rc == -ERESTART )
>          rc = hypercall_create_continuation(__HYPERVISOR_dm_op, "iih",
> @@ -628,16 +634,19 @@ long do_dm_op(domid_t domid,
>                unsigned int nr_bufs,
>                XEN_GUEST_HANDLE_PARAM(xen_dm_op_buf_t) bufs)
>  {
> -    struct xen_dm_op_buf nat[MAX_NR_BUFS];
> +    struct dmop_args args;
>      int rc;
>
> -    if ( nr_bufs > MAX_NR_BUFS )
> +    if ( nr_bufs > ARRAY_SIZE(args.buf) )
>          return -E2BIG;
>
> -    if ( copy_from_guest_offset(nat, bufs, 0, nr_bufs) )
> +    args.domid = domid;
> +    args.nr_bufs = nr_bufs;
> +
> +    if ( copy_from_guest_offset(&args.buf[0], bufs, 0, args.nr_bufs) )
>          return -EFAULT;
>
> -    rc = dm_op(domid, nr_bufs, nat);
> +    rc = dm_op(&args);
>
>      if ( rc == -ERESTART )
>          rc = hypercall_create_continuation(__HYPERVISOR_dm_op, "iih",
--
Julien Grall

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